The increasing number of difficult Extended Reach Drilling (ERD) applications in recent years has emphasized the need for reducing drill string drag. Drill string drag can substantially limit weight on bit and negatively effect directional control.
An improved type of drill pipe deployed Non-Rotating Drill Pipe Protector (NRDPP) has been developed that was found, both in laboratory tests and in actual down-hole drilling/sliding applications, to reduce drag inside casing up to 50% of that for bare drill pipe. This new tool incorporates existing NRDPP fluid bearing technology for torque reduction along with a modified geometry and the use of low-friction wear pads to reduce drag.
This paper describes the design and testing of the new "Low-Drag" NRDPP and provides a detailed discussion of three different wells that were drilled using this new tool for the purpose of providing drag, torque, and casing wear reduction. The wells, drilled by major oil companies in different regions of the world, were of varying profiles and possessed a unique set of operational circumstances.
ERD has become a common practice throughout the world as a means to reach a maximum number of targets from a single location. In recent years there have been increasing demands on operators to drill farther and deeper, while maintaining a higher degree of directional control than ever before. There are many factors which can limit the success of difficult ERD wells, among the most important are the ability to manage torque, drag, and casing wear.
One effective means of managing torque and casing wear, which has been developed over the last ten years and is utilized throughout the drilling industry, is the drill pipe deployed NRDPP. Moore(1) et al. has described the development and testing of this technology and has detailed field case studies where such technology was utilized by major operators to achieve torque reductions of 10–30% as well as prevention of casing wear in ERD applications.
In many ERD applications, long horizontal or high angle hole sections must be drilled, requiring slide drilling (drilling with motor only) for extensive sections of the hole. In these applications, drill string drag can become a significant problem and may even result in the abandonment of a well short of the planned TD. Excessive drill string drag can limit weight-on-bit, contribute to drill string buckling, cause "stick-slip" effect along the drill string, and substantially reduce directional control.
For these reasons, an improved type of NRDPP has been developed that can, along with reducing torque and preventing casing wear, significantly reduce drill string drag. This new type of Low-Drag NRDPP has been tested extensively both in laboratory and actual down-hole applications for performance as well as durability. The Low-Drag NRDPP has been found to substantially reduce drill string drag inside casing (up to 50% of that for bare drill pipe) and has shown exceptional durability.
To date, Low-Drag NRDPPs have been run successfully on over 10 wells for major oil companies in the Gulf of Mexico, Offshore California, Western and Eastern Canada, South America, and the North Sea.
The low drag NRDPP consists of three primary components: the "sleeve", which is free to rotate with respect to the drill pipe, and two thrust bearing "collars" that are fixed to the drill pipe holding the sleeve in place axially with respect to the drill string. (See Figure 1). The Outer Diameter (O.D.) of the sleeve is designed to be larger than the drill pipe tool joint, providing stand-off between the tool joint and casing wall.
The two collars, top and bottom, are identical designs constructed of aluminum.The collars have a thrust bearing surface, which faces inward toward the sleeve, and a tapered lead-in facing away from the sleeve.